In a packet forwarding process, a packet forwarding device usually needs to perform, according to content of a packet, different forwarding actions such as layer 2 switching and layer 3 routing and forwarding. The different forwarding actions generally indicate that edit processing needs to be performed on the packet in different manners.
Therefore, packet edit processing is a quite elementary but extremely important function. Packet edit processing mainly refers to that a packet forwarding device sometimes needs to modify a received packet (for example, adding or deleting a particular-layer protocol header field of the packet, or changing a Time To Live (TTL) field of the packet) according to a forwarding requirement. Therefore, the packet edit processing may be seen as a generic term of a process of modifying and editing a received packet. Generally, a complex packet edit processing procedure may be seen as a combination of a plurality of basic packet editing operations. Basic packet editing operations may be classified into the following three types: inserting operations, deleting operations, and replacing operations. An inserting operation usually refers to inserting a segment of new data into the received packet, a deleting operation usually refers to deleting a segment of data from the received packet, and a replacing operation usually refers to replacing a segment of data in the received packet with new data. For example, forwarding of a packet S1 over an Ethernet may be seen as a combination of a series of packet editing operations, such as deleting an old Ethernet (Ethernet) header field from the packet S1, replacing a value of a TTL field of the packet S1 (for example, decrease the value of the TTL field by one), replacing a header checksum (checksum) field in an Internet Protocol (IP) header field of the packet S1, and inserting a new Ethernet packet header field into the packet S1.
In existing packet edit processing, packet edit processing is generally implemented by a processor, that is, actions of packet edit processing may be implemented by executing related programs by the processor. In this manner, packet data is generally stored in a consecutive address area, and a start address and an end address of the packet data are recorded. The processor directly moves and modifies the packet data according to operations that need to be performed. After processing is complete, the edited packet is sent out of the packet forwarding device. For example, it is assumed that the packet forwarding device receives a 64-byte Ethernet+IPv4 packet (that is, protocol header fields of the packet include an Ethernet header field and an IPv4 header field). In a packet edit processing procedure, it is required to add a Virtual Local Area Network (VLAN) tag and then output a 68-byte Ethernet+VLAN+IPv4 packet. In the packet edit processing procedure, a program in a packet editing part needs to first move data of the received packet from an address 12-64 to an address 16-68; however, in this process, at least (64−16)/4=12 processor instructions are needed, and in a process of writing 4-byte data of the VLAN tag into an address 12, one processor instruction is needed.
It is found, according to study and practice of the prior art, that complexity of instructions of editing packets in the prior art is generally high, packet edit processing such as inserting and deleting operations is quite slow because a large amount of data need to be moved, and as packet lengths increase, time required for inserting and deleting operations also increases.